The integrity of elections and referendums, both public and private, rests upon, among other things, very accurate counting or tabulating votes made by ballot. Typically machines are used to tally votes made by ballots, as manual counting is generally too slow slow and unreliable for most elections. It is easy to assume that these machines are perfectly accurate; and they generally are becoming so, with fewer ballots being rejected and requiring special processing. However, achieving this nearly perfect accuracy--and reliability--is a demanding task where the need, or desire, for quick "returns" is becoming overwhelming. Vote counting machines are expected to provide the same, or better, accuracy, while increasing the number of ballots that can be processed.
The task is further complicated when "marked" ballots are used. Marked ballots are preprinted with the names of candidates (though there is often available a choice for a write-in candidate) or other choices (i.e. "yes" or "no" to propositions) that are being voted on. Ballots are in essence a form of a multiple-choice questionnaire. A voter votes or selects a choice by making some sort of indication next to the printed name or choice. The marked ballot requires a pen or pencil be used to draw a mark on the ballot to indicate a vote or selection. Accurate counting of marked ballots requires optically scanning the ballots, reliably detecting or reading each and every hand written mark on a ballot and recognizing that it is a valid vote or choice.
There are numerous different methods and apparatus pertaining to optically scanning documents, and detecting and recognizing marks on them. Most use some sort of pre-printed form and a scanning device that is adapted to the particular format. For example, one such ballot format is that described in U.S. Pat. No. 4,813,708, which is hereby incorporated by reference. Next to a printed column of candidates or choices are printed two columns of timing or clocking marks placed horizontally apart. The clocking marks are in columns, each column being referred to as a clocking channel. The space between the columns is referred to a as mark channel. A vote is cast or a selection made by drawing or writing a mark in a space between a pair of timing marks next to the candidate or choice. Only a written mark occurring between a pair of timing marks is a valid vote that is counted. Any other stray marks are ignored.
The scanner that has been used to detect timing marks and written marks includes a read head that has tungsten lamps illuminating the ballot with infra-red light and three photo-Darlington phototransistors, aligned in a row, to sense infra-red light reflected from the surface of the ballot. A ballot to be scanned or read is transported past the row of phototransistors in a direction of the columns of the marks and perpendicular to the row of sensors. In other words, each of the three columns is scanned from the top of the ballot to the bottom. A lens focuses the image of the illuminated ballot on to the three phototransistors, with the image of each column of timing marks being focused with a lens onto one of the two outboard phototransistors and the image of the channel being focused onto the center phototransistor. The ink used for printing the timing marks and writing the marks absorbs infra-red light. Therefore, when a phototransistor senses a significant drop of brightness in the infra-red light reflected from the ballot, it is likely due to a passing mark. When all three photodetectors sense a drop in infra-red light, a mark indicating a valid vote has been detected and a vote is recorded.
Such a scanner has several disadvantages. First, although the use of timing marks significantly reduces the risk of detecting stray marks, the scanner is not able to distinguish in all situations between stray marks that may be written (accidently or intentionally) by a voter on the ballot and valid timing marks. Should stray marks in the timing channels be interpreted as false timing marks, the ballot must be rejected and hand counted. Second, most common pens do not use ink that absorbs infra-red light. Therefore, special pens with infra-red absorbing ink must be used to mark the ballots, making marked ballot systems less acceptable to voter jurisdictions.
Other disadvantages of this scanner involves its use of photo-Darlington phototransistors. Though their intrinsic gain is large, simplifying amplification circuitry in the read head and making it easier to detect a drop in their output level due to a mark absorbing the infra-red light, the gain varies greatly between individual phototransistors, even within the same production run. The difference in gain may be as great as a factor of 2. The large gain variations complicate the reliable detection of timing and vote marks.
It is also difficult to control what the phototransistors are looking at and, more particularly, the size of the mark that they are resolving. The phototransistors are placed in a package about the size of a grain of rice. The package includes a bead of glass over the light-sensitive silicon portion of the photo-Darlington transistors. Even though the photo-Darlington package is properly placed and mounted such that the image of a column of marks, as it is scanned, is incident on it, the bead of glass interferes with detection of the levels of light. The bead of glass is effectively a distorted lens, since it appears to have a poorly controlled geometry introduced by its manufacturing process. Consequently, a great deal of manufacturing time must be spent sorting and rotating the photo-Darlington transistors to find one that has sufficient sensitivity to changes in light incident on it.
Finally, the phototransistor's frequency response is slow. As the speed of the ballots being transported past the scanner, and so too the speed of the marks, are increased, the frequency of fluctuations of light indicating the presence of the marks begins reaches the ability of the phototransistor to respond to the fluctuations. The limit of the phototransistor's frequency response has been found to correspond to approximately 100 to 200 ballots per minute. The speed of counting ballots is therefore limited by use of the photo-Darlington phototransistors as sensors.